(503f) Application of Immobilized Carbonic Anhydrase Enzyme in a Carbonate-Based Absorption Process for Post-Combustion CO2 Capture

An Integrated Vacuum Carbonate Absorption Process (IVCAP) for post-combustion CO2 capture is being developed by the Advanced Energy Technology Initiative of the Institute of Natural Resource Sustainability at the University of Illinois at Urbana-Champaign. In the process, potassium carbonate (PC) is employed as a solvent. Due to the slow rate of CO2 absorption into PC solutions, the carbonic anhydrase (CA) enzyme is employed as a biocatalyst to promote the absorption. We have previously shown that the free enzyme CA has an acceptable activity under the IVCAP conditions. However, immobilization of the CA enzyme onto water-insoluble carriers could potentially provide an effective option for improving the thermal and chemical stabilities of the CA enzyme and preventing enzyme elution in a continuous system.

In this study, a bovine CA enzyme was immobilized on a Controlled Pore Glass (CPG) material (SA = 25 m2/g, pore diameter = 100 nm) based on a covalent binding approach. A two-step activation; activation with γ-aminopropyl triethoxysilane followed by glutaldehyde, of CPG was performed. The immobilization approach was optimized by controlling densities of the active groups during CPG activation, removal of the activating agent residues after CPG activation, quenching of surplus active groups on the CPG surface after coupling with the CA, and wet storage of the immobilized CA enzyme. The activity of the immobilized CA was measured using a p-nitrophenyl acetate (p-NPA) hydrolysis assay under various conditions of stirring rate, pH, and temperature. The immobilization factor (a ratio between the specific activity of the immobilized and the free enzyme) for the immobilized CA on the CPG reached 0.47 (p-NPA as a substrate), a value which is 30-50% higher than those reported in the literature. The enzyme loading obtained was about 7 mg CA/g CPG. A higher loading can be achieved by using CPG support materials with smaller pore diameters (<100 nm) to provide higher surface areas. The thermal stability of the immobilized CA enzyme is currently being evaluated at temperatures of 40°C and 50°C. The initial results show that the CA in the immobilized form is more stable than the free CA.

Work is in progress to test activated carbon, ceramics and celite as support matrices for CA immobilization, develop alternative immobilization methods, and evaluate the performance of the immobilized CA enzymes in a packed-bed column for absorption of CO2 into PC solutions. An update of these activities will also be included in the presentation.